Abstract: We show that the existence of the bullet cluster, 1E0657-56,
is incompatible with the prediction of the standard Lambda CDM
cosmology. The probability of finding the large infall velocity (3000 km/s)
necessary for explaining the X-ray and weak lensing data of 1E0657-56 is
between 3.3x10^{-11} and 3.6x10^{-9}. The existence of the bullet cluster
poses a serious challenge to LCDM cosmology, unless a lower infall
velocity solution for 1E0657-56 with <1800 km/s is found.